The background information is believed, at the time of the filing of this patent application, to adequately provide background information for this patent application. However, the background information may not be completely applicable to the claims as originally filed in this patent application, as amended during prosecution of this patent application, and as ultimately allowed in any patent issuing from this patent application. Therefore, any statements made relating to the background information are not intended to limit the claims in any manner and should not be interpreted as limiting the claims in any manner.
Polypropylene (PP) is a thermoplastic polymer used in a wide variety of applications and is the most widely used polymer for meltblown applications. This may be due to its processability, rapid crystallization, and ease of drawing into fine fibers.
Typically, most commercial available polypropylene is mostly isotactic with moderate crystallinity. Crystalline polypropylene is in alpha, beta and gamma crystal forms along with the smectic form in an amorphous state. The triclinic gamma form rarely forms under standard processing conditions. Isotactic PP generally crystallizes into a stable monoclinic alpha form under standard process conditions, sometimes with a very low content of the hexagonal beta form. Typical processes for obtaining an increased content of the beta crystals may include directional crystallization under a temperature gradient, shear induced crystallization, and with the use of specific beta nucleating agents.
The presence of higher levels of beta crystals in meltblown fibrous materials or mat of fibrous materials, may provide the fibrous materials with desired properties. Typical processes used for obtaining an increased content of beta crystals may not be easily adaptable to current meltblown processes or may not provide the fibrous materials with the desired properties.